fix: add timeout handling for subprocess wait [backport 2.21]

[github-actions]

Backport b518cfd from #12806 to 2.21.

After subprocess is opened, wait and kill if Timeout is exceeded to ensure zombie processes are killed.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

https://datadoghq.atlassian.net/browse/APMLP-313

[github-actions]

CODEOWNERS have been resolved as:

releasenotes/notes/fix-lib-injection-zombie-dc16ca6c8bf50edb.yaml       @DataDog/apm-python
lib-injection/sources/sitecustomize.py                                  @DataDog/apm-core-python

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-05-14 14:30:00

Comparing candidate commit 579e3f9 in PR branch backport-12806-to-2.21 with baseline commit 91b8f48 in branch 2.21.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 344 metrics, 2 unstable metrics.